Experiments in an Adaptable-Wall Wind Tunnel for V/STOL Testing.

Experiments were carried out, over a period of two years, in an Adaptable-Wall wind tunnel configured for testing of airplane models at very large lift. The program was intended especially to demonstrate Proof of Concept for this type of wind tunnel, in which the simulated stream vector is inclined appreciably to the tunnel axis. The measured inner flow is matched to the computed, updated outer flow by an iterative process. Wall-adaptation controls in this tunnel are vaned panels in the floor and ceiling of the working section and a variable-angle inlet nozzle. Velocity components are measured by a Laser-Doppler system using a fixed laser and movable optical components. The test model used in these experiments was a high-wing VSTOL configuration having full-span wing flaps with lower-surface blowing of their inboard portions. In all of the experiments reported here, the combination of angle of attack, flap setting, and flap blowing was such as to produce large flow deflection and severe wall interference in a conventional tunnel. The model configuration was always laterally symmetrical, and most runs were made under the assumption of symmetrical flow. The iterative procedure, based on measured control matrices, typically led to minimum matching-discrepancies root-mean-square values of about three percent of stream speed after about six iterations. It is estimated that this reflects residual errors at the model of about one percent of stream speed. It is concluded that these results constitute successful Proof of Concept. Suggestions are made regarding the directions of further development of this type of wind tunnel. Author